Phenanthrene derivatives for use in liquid-crystalline mixtures have already been disclosed in DE-A 19500768, WO 98/27043, WO 98/27035 or WO 99/24385.
However, since the development of liquid-crystal mixtures can in no way be regarded as complete, display manufacturers are interested in a wide variety of components for mixtures.
In particular, liquid-crystal mixtures are required which have a very broad operating temperature range, but also a very low threshold voltage, for example for use in automobiles, in which a temperature range from xe2x88x9240 to 100xc2x0 C. can easily occur, but also for portable devices such as mobile telephones and notebook PCs. Moreover, it appears that the tendency toward moving images can be realized with nematic liquid crystals only when the electrode separation of such LCDs is reduced, since the response times are inversely proportional to the square of the electrode separation. This in turn inevitably results in a reduction in brightness and contrast, unless liquid-crystal mixtures having a high optical anisotropy (delta n) value are used. However, materials having a high optical anisotropy usually have high viscosities as well and are thus unfavorable for the objective intended.
There is thus a need for novel, suitable liquid-crystal mixtures and mixture components for these which have a high clearing point and a high optical anisotropy and at the same time have a relatively low rotational viscosity.
It is therefore the object of the present invention to provide novel components for use in nematic or cholesteric liquid-crystal mixtures which have positive dielectric anisotropy values combined with a favorable viscosity/clearing point ratio. Moreover, the compounds should have a high light and UV stability and thermal stability. They should furthermore be suitable for realizing high voltage holding ratios (VHR). They should also be readily obtainable synthetically and thus potentially inexpensive.
It has now been found that these requirements are satisfied in a particular manner by compounds of the formula (I)
R1xe2x80x94Axe2x80x94Z1xe2x80x83xe2x80x83(I)
in which:
R1 is an alkyl radical having 1 to 8 carbon atoms or an alkenyl radical having 2 to 8 carbon atoms, where, in each case, one (nonterminal) xe2x80x94CH2xe2x80x94 group may also be replaced by xe2x80x94Oxe2x80x94 or xe2x80x94C(xe2x95x90O)Oxe2x80x94 and/or one or more H may be replaced by F
A is phenanthrene-2,7-diyl or 9,10-dihydrophenanthrene-2,7-diyl
Z1 is F, OCHxF3xe2x88x92x or CHxF3xe2x88x92x, where, in each case, x is 0, 1 or 2, OC2HzF5xe2x88x92z or C2HzF5xe2x88x92z, where, in each case, z is 0, 1, 2, 3 or 4, CHxe2x95x90CF2 or Cl,
with the proviso that 2-fluoro-7-methoxy-phenanthrene is excluded.
Preference is given to those compounds of the formula (I) in which
R1 is an alkyl radical having 2 to 7 carbon atoms or an alkenyl radical having 2 to 7 carbon atoms, where, in each case, one (nonterminal) xe2x80x94CH2xe2x80x94 group may also be replaced by xe2x80x94Oxe2x80x94 and/or one or more H may be replaced by F
A is phenanthrene-2,7-diyl or 9,10-dihydrophenanthrene-2,7-diyl
Z1 is F, OCF3, CF3, OCHF2, CHF2.
Particular preference is given to those compounds of the formula (I) in which
R1 is an alkyl radical having 2 to 7 carbon atoms or an alkenyl radical having 2 to 7 carbon atoms or an alkyloxy radical having 2 to 6 carbon atoms or an alkenyloxy radical having 2 to 6 carbon atoms
A is phenanthrene-2,7-diyl or 9,10-dihydrophenanthrene-2,7-diyl
Z1 is F, OCF3, CF3.
Very particular preference is given to those compounds of the formula (I) in which
R1 is a linear alkyl radical having 2 to 7 carbon atoms or a linear alkyloxy radical having 2 to 6 carbon atoms
A is phenanthrene-2,7-diyl
Z1 is F, OCF3, CF3.
Very particular preference is likewise given to those compounds of the formula (I) in which
R1 is a linear alkyl radical having 2 to 7 carbon atoms or a linear alkyloxy radical having 2 to 6 carbon atoms
A is 9,10-dihydrophenanthrene-2,7-diyl
Z1 is F, OCF3, CF3.
Special preference is given to
2-ethyl-7-fluoro-phenanthrene
2-fluoro-7-propyl-phenanthrene
2-butyl-7-fluoro-phenanthrene
2-fluoro-7-pentyl-phenanthrene
2-fluoro-7-hexyl-phenanthrene.
Special preference is likewise given to
2-ethyl-7-fluoro-9,10-dihydrophenanthrene
2-fluoro-7-propyl-9,10-dihydrophenanthrene
2-butyl-7-luoro-9,10-dihydrophenanthrene
2-fluoro-7-pentyl-9,10-dihydrophenanthrene
2-fluoro-7-hexyl-9,10-dihydrophenanthrene.
The compounds of the formula (I) are used in liquid-crystal mixtures, preferably in nematic or cholesteric liquid-crystal mixtures. The liquid-crystal mixtures of the invention comprise at least one compound of the formula (I), preferably in an amount of 1 to 40% by weight, based on the liquid-crystal mixture. They preferably comprise at least 3 further components. The invention also provides a liquid-crystal display comprising these liquid-crystal mixtures.